Producing metallic magnesium from a



United States Patent Ofifice 3,114,627 Patented Dec. 17, 1963 PRODUCING METALLIC MAGNESIUM FROM A MAGNESIUM OXIDE CONTAINING MATERIAL Kozo Aoyama, Tokyo, Japan, assignor to Asahi Kasei Kogyo Kabushiki Kaisha, Osaka, Japan, a corporation of Japan No Drawing. Filed May 24, 1960, Ser. No. 31,273

Claims priority, application Japan Dec. 16, 1959 Claims. (Cl. 7567) This invention relates to a method of producing metallic magnesium from a magnesium oxide containing material by thermal reduction. There are various reports and literatures in connection with laboratory or industrial scale plant production of metallic magnesium by adding ferrosilicon to a magnesium oxide-containing material and heating the mixture under reduced pressure thereby to effect reduction of the material. Pidgeons and Bagleys processes (reaction temperature 11501250 C.) are typical for large-scale production. The former process is an outerheating, smaller volume and shortercycle system while the latter process is an inner-heating, larger-volume and longer-cycle system. Pidgeon process is more familiar because of the fact that it can use as heat-source a cheap fuel such as natural gas or heavy oil, and the apparatus is simpler and can be more safely operated, than in the Bagley process, although the heat efiiciency is inferior to the latters process. Pidgeons process, however, suffers, among other drawbacks, from the fact that a heat-proof retort made of special steel causing high wear and tear expense, must be used and that the capacity per retort is extremely low. Recently, the Beaudean process has been developed by Pechiney in France. This process has greater capacity per retort than that of Pidgeon, and is a shorter-cycle system. When magnesium oxidecontaining material of dolomite is reduced with ferrosilicon, slag of 2CaO-Si0 is formed, the melting point of which is 2130 C. This process comprises the addition of alumina to the system of calcined dolomite and ferrosilicon in order to reduce the melting point of the slag. The residue or slag thus obtained consists of silicoaluminate of lime, melting at about 1500 C. In Beaudean process, reaction temperature is 1500-l600 C. and the reactants are in the form of fluid throughout the reaction, so that capacity per retort is improved. The residue has good electro-conductivity, and consequently heat sulficient to maintain the thermal reduction reaction may be supplied by directly charging with electric current thereto. Unreacted ferrosilicon in the form of fluid is readily separable from the slag due to gravity dilference. However, the fact that the ore in Beaudean process is restricted to dolomite yields unavoidably a slag having a mole ratio of CaO/SiO of not less than 2. In order to provide a slag having lower melting point and electro-conductivity, alumina must be added until the A1 0 /SiO mole ratio in slag is not less than 0.3. According to a pamphlet issued by Pechiney Company, alumina is required in an amount of 750 kg. per metallic magnesium, so that the mole ratio of Al O /SiO in slag will be about 0.6. It is considered that the reaction follows the chemical equation: 2(CaOMg0) +(Fe)Si+O.6 A1 0 It will be seen from the above equation that a large amount of slag-forming materials such as lime and alumina must be added to magnesium oxide and ferrosilicon. 1 mole of lime and 0.3 mole of alumina are required in excess for producing 1 mole of metallic magnesium. Calcined materials of 6-7 tons must be charged to produce 1 ton of metallic magnesium, and accordingly electric power consumption in operation inevitably increases.

The present invention is an improvement of Beaudean process. I have discovered a method for the efiicient and economic production of metallic magnesium Without requiring such excess in amounts of slag-forming materials as the Beaudean process.

An object of the present invention is to provide a method of producing metallic magnesium from magnesium oxide-containing materials wherein an amount of the oxide materials required to produce a unit weight of the metal is greatly reduced compared with that required by Beaudean, thereby resulting in a reduction of the production costs.

Another object of the present invention is to produce metallic magnesium without adding alumina which is one of slag forming materials in Beaudean. The other object of the present invention is to produce metallic magnesium from magnesia in sea water.

I have never found that a slag having 44-64% by weight of SiO 30-53% by weight of CaO and 314% by weight of MgO, melts at a temperature less than 1450 C. and has better electroconductivity when fused, than that of Beaudean. Intrinsic electric resistances at various temperatures of the slag having the above mentioned composition are given in the table below.

TABLE 1 Beaudean The present The present process according to my invention is carried out in conformity with the following chemical equation: 2MgO+(Fe)Si+mCaO+nMgO SiO mCaO and nMgO form the slag. From the above equation, it will readily be seen that the slag-forming material such as lime and magnesia are employed as little as possible and, furthermore, 11o expensive alumina is required.

A magnesiumoxide containing material suitable in the present invention is magnesia produced from sea water. Such magnesia is readily available so that the present process does not depend upon the use of dolomite ore. As seen from the above Equation 2, the mole ratio of CaO to MgO in the charge feed, i.e., m:(2+n), according to Equation 2 above, must be about 0.26-0.56, for this reason, dolomite is rather undesirable, because it is mainly composed of CaO-MgO, corresponding to a molar ratio of 1:1. The less the amount of CaO in the MgO- containing material is, the better. However, if dolomite is used, magnesia obtained from sea water is admixed so that CaO to MgO becomes 0.26-0.56. Ferrosilicon and lime which are slag-forming materialsv are common ones, and any of the commercially available materials may be used.

The present process is carried out in a graphite crucible at a temperature of 1500l600 C. The pressure in the reaction zone is preferably 0.15 .0 mm. Hg. The heating up of the charge as well as the maintenance of the reaction temperature is conducted by directly passing an electric current through the charge or molten slag. On the basis of the above Equation 2, 0.5 mole of CaO and 0.079 mole of MgO are theoretically required as slag forming materials per mole of produced metallic magnesium to form a slag having 49% SiO 45.8% C210 and 5.2%

MgO. In practice the amount of residual, unreacted MgO enough to supply the necessary amount of 0.079 mole of i What I claim is: 1. A process for manufacturing metallic magnesium by adding ferrosilicon to a magnesium oxide-containing MgO. It will be seen from a comparison of the above material and heating under reduced pressure to effect reequations of the above Equations of (1) and (2), that 5 duction, which comprises preparing a mixture which is 0.5 mole, i.e. half of the CaO and 0.3 mole of the A1 0 substantially free from aluminum, consisting essentially required in the Beaudean process (1) are not required for of a magnesium oxide-containing material, ferrosilicon carrying out the present process (2) according to my inand lime wherein, in which mixture the molar ratio of vention. The theoretical amounts of charge required magnesium oxide to silicon is approximately 2:1 and that per ton of ferrosilicon is used. That is, the amount of of calcium oxide to magnesium oxide is about 0.26 to charge in the present process is about 55% of that of 0.56, heating up to 1450-1500 C. and then raising the Beaudean. Accordingly, the cost of production in the temperature to 1600 C. to effect liquid phase reduction, present process is considerably reduced. This is the most while maintaining a pressure of about 0.1 to 5.0 mm. Hg, favorable feature of the present process. When magthereby forming magnesium vapor and a molten slag nesium oxide containing materials of dolomite are used consisting of 44 to 64% by weight of SiO 30 to 53% as MgO component in Equation 2, magnesium oxide proby weight of C210 and 3 to 14% by weight of MgO, coolduced from sea water is added thereto, and then the necesing the magnesium vapor to recover metallic magnesium sary amount of CaO is added in accordance with Equaand separating ferrosilicon in the molten phase by gravity tion 2. diflerence from the molten slag thereby recovering the The purity of the metallic magnesium produced by the ferrosilicon. present process is about 99.9%, and Fe as impurity is 2. A process according to claim 1 wherein magnesia contained therein in amounts up to about 0.002%. recovered from sea water is mixed with dolomite in such For the purpose of giving those skilled in the art a better amounts that the aforesaid ratio of CaO to MgO equal understanding of the invention, the following illustrative to about 0.26 to 0.56 is obtained. examples are given: 3. In a process for manufacturing metallic magnesium Example 1 by thermal reduction of calcium oxide and magnesium In accordance with the Equations 1 and 2, respectively oxide-containing materials and ferrosilicon, and condenspulverized magnesia (grade: 95.1%), pulverized ferromg vaphr of magheslhm Pmhhced h the redhchoh h silicon (grade: 76.7%), lime (grade: 98.2%) and alumi- IeCOVeFmg 5 magnsmme the P whlch na (grade: 99.9%) were mixed together and briquetted. comPrlses Prepanhg mlxthre 5 f h h The mixing Was conducted assuming that the reaction calcium oxide, magnesium oxide and ferros1l1con, in which ciency between magnesia and ferrosilicon was 80%. In the B1019 fatfo f C ZMgO ranges from about 0.26 to case of (2), no addition of Mgo to that fed to initiate 0.56 and which is substantially free from alumlnum, and the reaction is required once the reaction starts, because r heahhg S mature to fusloh at a temperature h h MgO left in the slag is enough to maintain the reaction. F 1600 redhchd PTCSSUFC, the amount of slhcoh When m is 1 and n is 0.158 in Equation 2, the composim the fehrohlhcoh hehlg shihceht to Pmdhce a molten tion of slag thus produced will be $10 49%, CaO 45.8% Slag conslstmg essfintlally of of S102, and o 52% of CaO and 314% of MgO and having a melting point The briquettes were charged into graphite crucibles below 5 Cw and magheslhm 'f P respectively, and heated for min. at a reduced presh lmprhvemeht f to F h whfch the sure of mm For initial 30 minutes the magnesium oxide-containing material is magnesia obquettes were heated at 1500 C., and during the followtamed Sea watch ing 30 minutes at 1600 C. Both briquettes were comh 'lmprofemeht ficeordlng C1311? 3, Whlch pletely fused at 150045400 0 Metallic magnesium v dolomite 1s admixed with magnesia obtained from sea was obtained in a condensation cylinder mounted on the Water in Such Proportions that the aforesaid molar ratio graphite crucible. The results were shown in Table 2 0f CaOIMgO in the resulting mixture of about to below. 0.56 is obtained.

TABLE 2 Charge Mg Charge/ MgO ob- Mg. reaction taincd obtained ethciency, MgO Fc-Si 0210 A; Total percent Boaudean process. 106 45.8 114.2 61.8 327.8 55.2 5.94 91.3 The present 106 45.8 57.1 208.9 55.0 3.80 00.5

From the above table, it will be seen that materials of charge per produced metallic magnesium in the present process are considerably less than Beaudean process, that 60 References Cited in the file of this patent UNITED STATES PATENTS 2,934,423 Bretschneider et al Apr. 26, 1960 2,971,833 Artru et al Feb. 14, 1961 FOREIGN PATENTS 727,038 Great Britain Mar. 30, 1955 

1. A PROCESS FOR MANUFACTURING METALLIC MAGNESIUM BY ADDING FERROSILICON TO A MAGNESIUM OXIDE-CONTAING MATERIAL AND HEATING UNDER REDUCED PRESSURE TO EFFECT REDUCTION, WHICH COMPRISES PREPARING A MIXTURE WHICH IS SUBSTANTIALLY FREE FROM ALUMINUM, CONSISTING ESSENTIALLY OF A MAGNESIUM OXIDE-CONTAINING MATERIAL, FERROSILICON AND LIME WHEREIN, IN WHICH MIXTURE THE MOLAR RATIO OF MAGNESIUM OXIDE TO SILICON IS APPROXIMATELY 2:1 AND THAT OF CALCIUM OXIDE TO MAGNESIUM OXIDE IS ABOUT 0.26 TO 0.56, HEATING UP TO 1450*-1500*C. AND THEN RAISING THE TEMPERATURE TO 1600*C. TO EFFECT LIQUID PHASE REDUCTION, WHILE MAINTAINING A PRESSURE OF ABOUT 0.1 TO 5.0MM. HG., THEREBY FORMING MAGNESIUM VAPOR AND A MOLTEN SLAG CONSISTING OF 44 TO 64% BYH WEIGHT OF SIO2, 30 TO 53% BY WEIGHT OF CAO AND 3 TO 14% BY WEIGHT OF MGO, COOLING THE MAGNESIUM VAPOR TO RECOVER METALLIC MAGNESIUM AND SEPERATING FERROSILICON IN THE MOLTEN PHASE BY GRAVITY DIFFERENCE FROM THE MOLTEN SLAG THEREBY RECOVERING THE FERROSILICON. 